1. Field of the Disclosure
The present disclosure relates to a capacitance-type proximity sensor device that detects the approach of an object to be detected, and more particularly, to a capacitance-type proximity sensor device that can be appropriately used in a portable apparatus and an electronic apparatus using the same.
2. Description of the Related Art
As a device that detects an object to be detected, such as the human body, a capacitance-detection-type proximity sensor has been proposed which shields capacitance variation (external noise) in the directions other than a detection target direction and improves detection sensitivity (for example, see WO/2004/059343). The capacitance-detection-type proximity sensor includes two detecting electrodes that are arranged such that capacitances are formed between a ground potential and the detecting electrodes and shielding electrodes that are arranged around the two detecting electrodes and shield the detecting electrodes from a capacitance variation in the directions other than a detection direction. A detecting circuit that detects a difference value between output signals is connected to the two detecting electrodes and a shielding voltage applying circuit that applies a voltage is connected to the shielding electrodes.
When the object to be detected, such as the human body, is detected, the shielding voltage applying circuit applies a voltage to the shielding electrodes such that the shielding electrodes and the two detecting electrodes have the same potential. In this state, when the object to be detected approaches the detecting electrodes, capacitances Ca and Cb formed between the detecting electrodes and a ground potential are changed and signals corresponding to the capacitances Ca and Cb are output from the detecting electrodes. The difference value between two output signals is detected by the detecting circuit. In this way, the approach of the object to be detected is detected.
However, in recent years, the capacitance-detection-type proximity sensor has been applied to, for example, portable apparatuses and has been used when the user holds the portable apparatus with the hand. In this case, the capacitance-detection-type proximity sensor is used to detect an object to be detected with the hand of the user, which is a portion of the body of the user and also serves as the object to be detected, placed in the vicinity of the capacitance-detection-type proximity sensor. Therefore, for example, the holding position and holding state of the portable apparatus by the hand have a great effect as external noise on the output signal from the capacitance-type proximity sensor.
However, in the capacitance-detection-type proximity sensor disclosed in WO/2004/059343, external noise in the directions other than the detection target direction is not sufficiently reduced and it is difficult to obtain a sufficient performance when the capacitance-detection-type proximity sensor is used in, for example, a portable apparatus. In addition, for example of, when the usage environment of the portable apparatus is changed, it is necessary to calibrate the reference value of the output signal according to external noise in the usage environment.